1. Field of the Invention
The present invention relates to a circuit device having a booster circuit therein.
2. Description of the Related Art
Generally, a boosting DC/DC converter is known as an apparatus for boosting a DC supply voltage from a power supply that supplies electric power, to a desired DC voltage level. In recent years, there are an increasing number of power supplies where the voltage of electric power to be supplied falls below a starting voltage of the DC/DC converter. A method was proposed where an auxiliary power supply for starting the DC/DC converter by such power supply is attached to the power supply.
FIG. 4 is a circuit diagram showing a circuit device provided with a conventional booster circuit.
This circuit device includes: a power supply 101 for supplying electric power; a first booster circuit (auxiliary power supply) 102, started by the power, which converts the power into a voltage higher than the voltage of this power; and a second booster circuit (DC/DC converter) 103, started by a first boosted power, which converts the power into a second boosted power higher than the voltage of this power and which continues the operation under this second boosted power. The circuit device further includes: a load circuit 104, operated by the second boosted power, which achieves a desired function; a capacitor 105 which charges the first boosted voltage; a voltage detection circuit 106 which detects the voltage of the capacitor 105 and outputs a voltage detection signal according to the detected voltage of this capacitor 105; and a switch element 107 controlled by the voltage detection signal. The starting voltage of the first booster circuit 102 is lower than that of the second booster circuit 103. The power charged in the capacitor 105 is supplied to the second booster circuit 103 via the switch element 107 to start the second booster circuit 103. When it is determined by the voltage detection circuit 106 that the voltage of the capacitor 105 is greater than or equal to a predetermined voltage, the switch element 107 is turned on; and the power stored in the capacitor 105 with the switch element 107 being turned off is supplied to the second booster circuit 103 to start the second booster circuit 103.
In such a conventional electronic apparatus, after the power sufficient for starting the second booster circuit 103 is charged into the capacitor 105 by the first booster circuit 102, the switch element 107 is turned on to start the second booster circuit 103 by the power stored in the capacitor 105. Once the second booster circuit 103 is started, an internal circuit is operated by itself. Thus, the switch element 107 is turned off and the supply of the voltage stored in the capacitor 105 to the second booster circuit 103 is stopped. Thereby, the power of the power supply 101 can be boosted up to the second boosted power and the electric power can be supplied to the load circuit 104 so as to operate the load circuit 104.
Though not described in the configuration of the above-mentioned conventional electronic apparatus (circuit device), an output smoothing capacitor of a large capacitance value is generally used and connected between an output terminal 127 of the second booster circuit (DC/DC converter) 103 and the load circuit 104. In recent years, the compactness and the high density are strongly desired in such electronic apparatus (circuit device). However, the size of circuit components, such as a DC/DC converter, an auxiliary power supply, a switch element and a capacitor, which constitute the electronic apparatus, places restrictions and limits the compactness and high density of the circuit device.